Blast furnaces of the bell less Top® design comprise a chute transmission gearbox between the top cone of the blast furnace and the material charging hoppers. Such a chute transmission gearbox comprises ball bearings for the rotation of the associated rotary chute, which is used to evenly distribute charge material into the blast furnace. The correct installation of the chute transmission gearbox on the top of the blast furnace is of particular importance. An incorrect installation may have devastating consequences on the correct functioning of the ball bearings, and consequently of the chute transmission gearbox. Indeed, the seat receiving the chute transmission gearbox must be precision engineered and must satisfy rather strict tolerances regarding flatness.
Generally, the top cone of the blast furnace is provided with a top cone ring for receiving a connection flange of the chute transmission gearbox thereon. Both the top cone ring and the connection flange must be machined so that they fit together perfectly. In order to further avoid any gas from escaping between the top cone ring and the chute transmission gearbox, a sealing compound is applied on the top cone ring before installation. In view of the strict tolerances that have to be respected, it is generally necessary to adapt the top cone ring during erection or revamping of the blast furnace. Such on-site adaptation of the top cone ring is rather time-consuming and thus expensive. In some circumstances it may furthermore be particularly difficult to meet the necessary tolerances, thus with the risk of installing the chute transmission gearbox without respecting the necessary tolerances and therefore endangering the correct functioning of the rotary chute.